1 files changed, 123 insertions, 0 deletions
diff --git a/services/core/java/com/android/server/TwilightCalculator.java b/services/core/java/com/android/server/TwilightCalculator.java
new file mode 100644
index 0000000..a5c93b5
--- /dev/null
+++ b/services/core/java/com/android/server/TwilightCalculator.java
@@ -0,0 +1,123 @@
+/*
+ * Copyright (C) 2010 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.server;
+
+import android.text.format.DateUtils;
+import android.util.FloatMath;
+
+/** @hide */
+public class TwilightCalculator {
+
+    /** Value of {@link #mState} if it is currently day */
+    public static final int DAY = 0;
+
+    /** Value of {@link #mState} if it is currently night */
+    public static final int NIGHT = 1;
+
+    private static final float DEGREES_TO_RADIANS = (float) (Math.PI / 180.0f);
+
+    // element for calculating solar transit.
+    private static final float J0 = 0.0009f;
+
+    // correction for civil twilight
+    private static final float ALTIDUTE_CORRECTION_CIVIL_TWILIGHT = -0.104719755f;
+
+    // coefficients for calculating Equation of Center.
+    private static final float C1 = 0.0334196f;
+    private static final float C2 = 0.000349066f;
+    private static final float C3 = 0.000005236f;
+
+    private static final float OBLIQUITY = 0.40927971f;
+
+    // Java time on Jan 1, 2000 12:00 UTC.
+    private static final long UTC_2000 = 946728000000L;
+
+    /**
+     * Time of sunset (civil twilight) in milliseconds or -1 in the case the day
+     * or night never ends.
+     */
+    public long mSunset;
+
+    /**
+     * Time of sunrise (civil twilight) in milliseconds or -1 in the case the
+     * day or night never ends.
+     */
+    public long mSunrise;
+
+    /** Current state */
+    public int mState;
+
+    /**
+     * calculates the civil twilight bases on time and geo-coordinates.
+     *
+     * @param time time in milliseconds.
+     * @param latiude latitude in degrees.
+     * @param longitude latitude in degrees.
+     */
+    public void calculateTwilight(long time, double latiude, double longitude) {
+        final float daysSince2000 = (float) (time - UTC_2000) / DateUtils.DAY_IN_MILLIS;
+
+        // mean anomaly
+        final float meanAnomaly = 6.240059968f + daysSince2000 * 0.01720197f;
+
+        // true anomaly
+        final float trueAnomaly = meanAnomaly + C1 * FloatMath.sin(meanAnomaly) + C2
+                * FloatMath.sin(2 * meanAnomaly) + C3 * FloatMath.sin(3 * meanAnomaly);
+
+        // ecliptic longitude
+        final float solarLng = trueAnomaly + 1.796593063f + (float) Math.PI;
+
+        // solar transit in days since 2000
+        final double arcLongitude = -longitude / 360;
+        float n = Math.round(daysSince2000 - J0 - arcLongitude);
+        double solarTransitJ2000 = n + J0 + arcLongitude + 0.0053f * FloatMath.sin(meanAnomaly)
+                + -0.0069f * FloatMath.sin(2 * solarLng);
+
+        // declination of sun
+        double solarDec = Math.asin(FloatMath.sin(solarLng) * FloatMath.sin(OBLIQUITY));
+
+        final double latRad = latiude * DEGREES_TO_RADIANS;
+
+        double cosHourAngle = (FloatMath.sin(ALTIDUTE_CORRECTION_CIVIL_TWILIGHT) - Math.sin(latRad)
+                * Math.sin(solarDec)) / (Math.cos(latRad) * Math.cos(solarDec));
+        // The day or night never ends for the given date and location, if this value is out of
+        // range.
+        if (cosHourAngle >= 1) {
+            mState = NIGHT;
+            mSunset = -1;
+            mSunrise = -1;
+            return;
+        } else if (cosHourAngle <= -1) {
+            mState = DAY;
+            mSunset = -1;
+            mSunrise = -1;
+            return;
+        }
+
+        float hourAngle = (float) (Math.acos(cosHourAngle) / (2 * Math.PI));
+
+        mSunset = Math.round((solarTransitJ2000 + hourAngle) * DateUtils.DAY_IN_MILLIS) + UTC_2000;
+        mSunrise = Math.round((solarTransitJ2000 - hourAngle) * DateUtils.DAY_IN_MILLIS) + UTC_2000;
+
+        if (mSunrise < time && mSunset > time) {
+            mState = DAY;
+        } else {
+            mState = NIGHT;
+        }
+    }
+
+}